Furnace



F. C). HESS March 19, 1963 FURNACE INVENTOR.

FREDERIC O. HESS 2 Sheets-Sheet l XAUWJ 5AM FIG. 2.

FIG. 1.

United States Patent 3,081,988 FURNACE Frederic O. Hess, Philadelphia, Pa., assignor to Selas Corporation of America, Dresher, Pa., a corporation of Pennsylvania Filed Dec. 9, 1959, Ser. No. 858,410 7 Claims. (Cl. 2664) The present invention relates to furnaces, and more particularly to furnace-s of the salt bath typethat are used for heat treating or melting of metal.

In most salt bath furnaces there is the problem of spattering hot salt when work is inserted into and removed from the bath. A further problem is the draining of the hot salt from time to time, from the space in which the work is heated, when cleaning is necessary.

It is an object of the invention to provide a salt bath furnace in which the salt is removed from the work heating space when work is inserted into and removed therefrom. i It is a furtherobject of the invention to provide a furnace in which salt is heated to an even temperature and is circulated around the work while it is being heated.

In practicing the invention, there is provided a furnace having a salt melting area with a bottom on one level and a work heating area on a second and higher level. These areas are connected by passages through which the salt can be circulated. The salt is heated by a heating unit that can be raised and lowered in the salt melting area, thereby changing the level of the salt. Thus, when the heating unit is lowered into the melting area, the salt level is raised sufficiently for the salt to flow into the work heating area and cover work placedtherein. With such an arrangement, work can be placed on and removed from a dry hearth while the salt is continually being maintained at the desired temperature.

It is obvious thatthe apparatus could be used where other material than salt is to be used as the heating medium such as lead or some other metalfor example.

The various features of novelty which characterize my invention are pointed out with particularity in the W A 3,081,988 Patented Mar. 19, 1963 Salt for heating the work in the chamber 3 is heated and kept molten in chamber 1, and is circulated through the passages 8 and 9 between the two chambers so that the molten salt can heat work in chamber 3. The salt is heated and kept in its melted condition by means of a heating unit 12 which includes an inner refractory member 13, which has the same shape as the interior of chamber 1, but is smaller in size than that chamber. In the drawings, this chamber is shown as being cylindrical, but it could take any other desired shape. The refractory member is shorter than the depth of chamber 1, and is provided with a radially extending flange 14 which rests on the upper edge of the open chamber to close this chamber during the time the heating unit is in heating position as shown in FIG. 1. A shell 15 of an alloy steel, that will Withstand the temperatures encountered and which will not be harmed by the salt, surrounds and is spaced from the refractory cylinder. This shell is supported on flange 14 by means of bolts 16 which extend through the flange. These bolts have yokes 17 at their lower end, the arms of which extend on each side of the shell and are provided with openings through which a pin -18 extends. The position of the shell with respect to the refractory member 13 can be adjusted by nuts 19. Normally, the nuts will be adjusted to bring the shell up against spacers 21 which locate'the shell with respect to the refractory member, both axially and radially. The distance between the burners, described below, and the bottom of shell 15 can be varied to give as large a combustion space as is necessary or desired.

' The limiting position is to have the bottom of strucclaims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages. and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated an described a preferred embodiment of the invention.

In the drawings: i

FIG. 1 is a section through the furnace taken on line 11 ofFIG. 2,

'FIG. 2 is a section taken on line 2--2 of FIG. 1,

FIG. 3 is a section through a portion of the furnace taken on line 3--3 of FIG. 1, and FIG. 4 is a-section similar to FIG. 1 showing a modified form of the work chamber.

Referring to FIGS. 1 to 3 of the drawing, there is shown a furnace which includes a salt chamber 1 having a bottom 2 and a work heating chamber 3 having abottom 4 upon which there is placed a plate 5 forming a hearth to receive the work 6. It will be noted that the floor .of chamber 1 is considerably below the floor of chamber 3. These structures are made of refractory in accordance with ordinary furnace practice and are supported by a structural steel framework. The chambers purpose to be described.

ture 13'level with flange 14.

The heating unit is built around a structural steel frame 22, and the entire unit may be raised and loweredby cables 23 which are attached to the frame. These cables pass over a pulley 24 and are wound upon a drum 25 that is operated by a reversible motor (not shown). With this arrangement, the heating unit can be lowered into heating position shownin FIGS. 1 and 2 of the drawings, or it can be moved up to a position inwhich the entire unit is out of chamber 1 to give access to the salt therein for cleaning or replenishing the salt.

The heating unit is heated by a plurality of burners 26 which are shown herein as being of the radiant cup type and as being located at spaced points in the bottom of the refractory member. These burners are connected by a fuel supply manifold 27 that is in turn supplied by a flexible pipe 23 extending between the manifold and a gas supply pipe. The pipe 23 is sufficiently flexible so that it can be bent as the heating unit is raised and lowered. When the burners are fired, they serve to heat shell 15, which in turn transfers the heat to the salt. The most intense heat is, of course, directly in front of the burners on the bottom of the shell, but during operation of the apparatus, the hot products of combustion will flow through the space 29 between the refractory member and the shell, and will heat the entire surface of the shell j to a high temperature. The products of combustion'are exhausted from space 29 between the upper edge of the shella'nd flange '14. These products of combustion then flow through a space 31 across the top of chamber 3 and When the furnace is in operation, salt is circulated through-the passages S and 9 of the partition7 by means of a pair of paddle wheels 34 and 37 which rotate in opposite directions. Paddle wheel 34 is mounted on a shaft 35 and is driven by a motor 36 that is mounted on a suit- 3 able support outside of the furnace chamber. In a like manner, paddle wheel 37 is mounted on a shaft 38 and driven by a motor 39. It will be noted that the paddle wheels are at an elevation so that their shafts are above the side walls of chamber 3. Suitable slots are provided in cover 32 for the shafts to extend between the motors and the paddle wheels. A deflector 41 extends across the work chamber to direct the salt flow downwardly along surface 11 of passage 9, thereby to insure that there is a good circulation of the salt through work chamber 3.

In the operation of the furnace, the heating unit 12 is raised, and salt of the proper type and amount is placed in chamber 2. The burners in the unit are ignited, and the heating unit is gradually lowered. The hot bottom surface of shell will begin the melting process, and as the salt is melted, the heating unit can be lowered with the molten salt rising in chamber 1 around the shell. There is sufficient salt placed in the chamber so that when the heating unit is raised, the salt will have a lower level indicated by the line 42, which is just below the floor 4 of work chamber 3. When the salt is completely melted and the heating unit is in its low position shown in FIG. 1 of the drawing, the salt will havereached a level shown at 43, which is sufficient to cover the work 6 that has been placed in chamber 3. When the salt has melted and the furnace is operating, the paddle wheels rotating in oppo site directions will circulate salt through the work chamber and back to the heating chamber. Thus, the work is immersed in the salt, which is always kept at an optimum temperature by the circulating system. 'Furthermore, the exhaust gases from the burners passing over the top of salt in chamber 3 are sufficiently hot to prevent this. salt from chilling. The unit, therefore, keeps a constant salt temperature throughout the level of the salt in chamber 3.

Prior to heating a piece of work, cover 32 is lifted off the top of chamber 3 by means of a suitable ring 44, and the heating unit is raised to its elevated position. In so doing, the level of the salt in chamber 3 falls to a point below the floor of this chamber. The salt is maintained in a heated condition during this time by its engagement with the bottom portion of shell 15. The heating chamber is now empty of salt so that the work piece can be placed in chamber 3 and accurately positioned on hearth 5. This can be done in the open without any splashing of the molten salt over the surroundings. The top is then placed over chamber 3, and the heating unit lowered. During this latter operation, the salt level rises from below the floor of chamber 3 -to above the top of the work piece. The salt is then circulated while the piece is being heated. When the heating is finished, the heating unit can be raised in chamber 1 to lower the level of salt in chamber 3 so that the work is exposed for easy removal. It is noted that deflector 41 will serve to drive the salt downwardly through passages 9 so that a good circulation is obtained throughout the entire volume of the heating chamber.

In FIG. 4 of the drawing there is shown a form of the invention that can be used for melting metal and which is particularly adapted for the melting of aluminum chips. Referring to that FIGURE, it will be seen that the bottom of the work chamber indicated at 45 is sloping and is provided with an outlet spout 46 through which the molten metal can flow. Normally, this spout would be closed by a suitable stopper so that the metal would only be removed from time to time. It will also be noted, by referring to the FIGURE, that the lower passages 8 in partition 7 have been eliminated.

In the operation of this embodiment of the invention, the heating unit 12 is moved to the desired lower position, thereby raising the salt level in chamber 3 to a point indicated by line 47. This salt is circulated as described above by means of paddles 34 and 37. Aluminum chips, for example, are dropped to the work chamber through a spout 48 formed in top 32. These chips fall into the salt immediately in front of the paddles, and are moved 4 by them with the salt against deflector '41 so that they will be forced below the surface of the salt. Since the salt is above the melting temperature of the aluminum, and since the aluminum is heavier than the salt, the aluminum will be melted by the salt, and 'will sink below the surface. From time to time as additional aluminum is added to the bath, the heating unit 12 must be gradually raised in order to keep the level of the salt at 47, as this salt is displaced in the melting chamber by the addition of the aluminum. When the aluminum has reached a level substantially equal to the bottom of passage 9, it must be drained from the chamber to make place for the addition of more aluminum.

An arrangement of this type is of particular advantage in the melting of aluminum chips, since these chips individually will have a tendency to float on the surface of the salt, and thereby become oxidized. The chips in this case, however, are falling on the surface of the salt immediately in front of the paddle. They will be forced by the paddle against the deflector and will sink as they are being melted and before they have had time to become oxidized. Since the salt always floats on top of the aluminum, it is only necessary to raise the heating unit sufficiently for the salt to flow out of the melting chamber to expose the entire melt of aluminum. The chamber can then be drained and cleaned as is necessary from time to time. With this arrangement, the salt is automatically drained from the melting chamber prior to the time the aluminum is removed to leave an empty chamber when cleaning is necessary.

From the above description, it will be seen that the salt bath furnace described herein has the advantage of melting the salt in one chamber, which can be kept at an optimum temperature, and of heating the work in a second chamber. The arrangement is such that the work chamber can be emptied of salt so that the work can be placed into the chamber and removed therefrom easily and quickly, with no chance of hot salt being splashed over the surroundings. Although the apparatus is particularly adapted to be used for a salt bath furnace, it is obvious it could be used when other materials, such as a metal, is the heating medium. Such heating material is to be contemplated in the claims annexed hereto.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a salt bath furnace, structure forming a first chamber having a floor at one level in which work is to be heated, and a second chamber in which salt is to be melted having a floor at a lower level, a partition separating said chambers, said partition having passages therein at substantially the level of the floor of said first chamber through which salt may flow, a heating unit for the salt, and means to move said heating unit into and out of said second chamber thereby to displace salt in said second chamber through said passages to vary the level of the salt in said first chamber.

2. The combination of claim 1 in which said heating unit includes a burner and including a removable cover over said first chamber, and means to direct combustion gases from said burners between said first chamber and cover.

3. In a salt bath furnace, structure forming an open top heating chamber for the salt, a heating unit comprising a shell of heat conducting material of a size to be received in said chamber and means in said shell including a plurality of burners to heat said shell by the burners and combustion gases produced thereby, means to support said heating unit over said chamber for movement into and out of said chamber to heat the salt therein and to vary the level of the salt depending upon how far said heating unit is moved into said chamber, a second cham ber in which work to be heated is placed, and means forming passages to connect said chambers, said passages opening into said first chamber at a level between the maximum and minimum levels reached by the salt as said heating unit is moved into and out of said first chamber.

4. In a furnace, structure forming an open top chamber in which a material is to be melted, a heating element, means to mount said heating element for vertical movement into and out of said chamber, said heating element including an outer shell of heat conducting material having sides and a bottom and an inner member of refractory material of substantially the same shape as said' shell and spaced therefrom, a burner in said inner member operative to heat directly the bottom of said shell with the products of combustion from said burner flowing through the space between said inner member and shell to heat the sides of said shell, and means to raise and lower said heating element.

5. In a furnace, structure forming a chamber having a floor upon which work to be heated is placed, structure forming a reservoir for a heating fluid, the bottom of said reservoir being below said floor, means donning pass-ages between said chamber and said reservoir at substantially the level of said floor, a displacing element, means to move said element into and out of said reservoir to vary the level of the fluid therein from below to above said passages, whereby fluid can flow through said passages to said chamber to heat work therein, and means to heat the fluid in said reservoir. J

6. The combination of claim 5 in which said passage forming means has displaced passages between said chamber and reservoir, and means in said passages to circulate salt between said chamber and reservoir.

7. In a salt bath furnace, structure forming a first chamber in which metal is to be melted, a second chamber in which salt is to be melted, means forming a partition having a passage therein between said chambers, said passage being above the level of metal in said first chamber, means to circulate molten salt between said chambers through said passage, means through which metal to be melted can be introduced in said first chamber and below the salt therein, and means to maintain constant the level of the salt in said chambers as the salt is displaced by the addition of metal to said first chamber.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A SALT BATH FURNACE, STRUCTURE FORMING A FIRST CHAMBER HAVING A FLOOR AT ONE LEVEL IN WHICH WORK IS TO BE HEATED, AND A SECOND CHAMBER IN WHICH SALT IS TO BE MELTED HAVING A FLOOR AT A LOWER LEVEL, A PARTITION SEPARATING SAID CHAMBERS, SAID PARTITION HAVING PASSAGES THEREIN AT SUBSTANTIALLY THE LEVEL OF THE FLOOR OF SAID FIRST CHAMBER 